The anatomy, physiology, and pathologic processes that involve the central nervous system (CNS) make CNS tissue unique. The preservation of both the three-dimensional structural anatomy and the microanatomical relationships of neurons (whose function depends specific on spacial relationships with other neurons and other supporting cells), as well as the maintenance of properly oxygenated blood flow and the homogeneous ground substance matrix in which the neurons survive, are vital to the survival and function of the central nervous system tissues. Moreover, the inability of central nervous system cells to regenerate emphasizes the need to maximize survival of every possible neuron. For reasons such as these, treatment of both open and closed space pathology in the central nervous system is unique.
Among the clinical problems that threaten survival of CNS tissues, the control of central nervous system edema, infection, and blood supply are central. The brain responds to trauma and injury by collecting a significant amount of interstitial edema. Because the brain is enclosed in a closed space (the dura and skull), edema results in compression and compromise of the blood flood and nutritional performance of the CNS, which greatly impairs physiological recovery of the central nervous system and often of itself results in progression of compromise and death of the CNS parenchyma. Currently available treatments for reducing edema include agents to decrease vascular permeability (glucocorticoids: Dexamethasone, Prednisone, Methyl Prednisolone), diuretics, mechanical ventricular drainage, resection of the brain parenchyma, and extensive craniectomy. However, disadvantages to these treatments include poor results, complications from the drugs, and inconsistent results.
The need for rapid and effective treatment is also vital due to the disastrous consequences and high likelihood of rapid propagation of infection and edema in the CNS. At present there are few successful methods available to treat pathologies affecting the intracranial and intraspinal space, CNS parenchyma, and the surrounding structures. Where elsewhere tissues can be treated with dressing changes, the CNS is not amenable to this type of treatment because of its inaccessibility, precarious structure, propensity for infection, and progression of injury. There is evidence that inflammation and immunological response to central nervous system trauma and other pathology are of equal or greater long term consequences than the initial trauma or insult. The response of the CNS to decreased blood flow secondary to edema results in hypoxia and ischemia/reperfusion-mediated injury. These injuries contribute to the neuropathological sequella, which greatly contribute to the adverse outcome of head injury.
In addition, the brain requires a continuous supply of oxygenated blood to function and survive. Within three minutes of complete interruption of blood flow to the brain, irreversible brain damage results, though the brain can however remain viable and recover from reduced blood flow for more prolonged periods. There is evidence that focal areas of the brain can remain ischemic and relatively functionless for days and still recover. This finding has led to the concept of an ischemic zone, termed the penumbra or halo zone, that surrounds an area of irreversible injury. A secondary phenomena is the release of excitotoxins that are released locally by injured neurons, alterations in focal blood flow, and edema.
Cerebrovascular disease may be a result of: inadequate blood flow to the brain cells from decreased perfusion pressure, rupture of a blood vessel resulting in direct injury to the local brain area and by compression of adjacent tissue. Intrinsic disease of the brain blood vessels such as atherosclerosis, aneurysm, inflammation, etc. or a remote thrombus that lodges in the brain blood vessels from elsewhere such as the heart can produce cerebrovascular disease. A stroke is a term that defines a neurological injury that occurs as a result of some of these pathologic processes. Five percent of the population over 65 are affected by cerebrovascular diseases which are the third leading cause of death in the developed world. In addition, lifelong debility, inability to work and function in society and the family, and the frequent need for nursing home treatment often result. People affected by strokes usually have significant impairments for the rest of their lives.
A stroke in evolution, or progressive stroke, refers to a neurological deficit that progresses or fluctuates after the initial event. It is thought that this occurs because of progressive spasm or narrowing of the involved artery, development of cerebral edema around the initial injury, thrombus propagation as a result of decreased blood flow or release of local cytokines from injured brain cells. Fortunately there are some communications between vessels in the brain called collateral circulation. Supplying blood from these collateral vessels may prevent death of brain cells in the ischemic zone.
In cases of intracranial hemorrhage, the hemorrhage usually begins as a small mass that grows in volume by pressure dissection and results in displacement and compression of adjacent brain tissue. Edema in the adjacent compressed tissue around the hemorrhage may lead to a mass effect and a worsening of the clinical condition by damaging a larger area of brain tissue. Edema in the adjacent brain may cause progressive deterioration usually seen over 12 to 72 hours. The occurrence of edema in the week following the intracerebral hemorrhage often worsens the prognosis, particularly in the elderly. The tissue surrounding the hematoma is displaced and compressed but is not necessarily fatally compromised. Improvement can result as the hematoma is resorbed and the involved tissue regains function.
Treatment of these conditions has been disappointing. Surgical decompression of hemorrhage can be helpful in some cases to prevent irreversible compression. Agents such as mannitol and some other osmotic agents can reduce intracranial pressure caused by edema. Steroids are of uncertain value in these cases, and recently hyperbaric oxygen has been proposed.
Thus, though the application negative (or sub-atmospheric) pressure therapy to wounded cutaneous and subcutaneous tissue demonstrates an increased rate of healing compared to traditional methods (as set forth in U.S. Pat. Nos. 5,645,081 and 5,636,643, 7,198,046, and 7,216,651 as well as US Published Application Nos. 2003/0225347, 2004/0039391, and 2004/0122434, the contents of which are incorporated herein by reference), there remains a need for devices and methods specifically suited for use with the unique tissues of the central nervous system.